Temporal dynamics of spectral reflectance and vegetation indices during canola crop cycle in southern Brazil

ABSTRACT: The objective of this study was to characterize the variability of spectral reflectance and temporal profiles of vegetation indices associated with nitrogen fertilization, crop cycle periods, and weather conditions of the growing season in canola canopies in southern Brazil. An experiment was carried out during the 2013 and 2014 canola growing seasons at EMBRAPA Trigo, Passo Fundo, state of Rio Grande do Sul, Brazil. The experiment was conducted in a randomized block design with four replications. Five doses of nitrogen top dressing were used as treatments: 10, 20, 40, 80, and 160kg ha-1. Measurements were obtained with the spectroradiometer positioned above the canopy, to construct spectral reflectance curves for canola and establish temporal profiles for several vegetation indices (SR, NDVI, EVI, SAVI, and GNDVI). In addition, data on shoot dry matter were obtained and phenological stages were determined. The spectral reflectance curves of canola were reported to change with canopy growth and development. Temporal profiles of vegetation indices showed two maximum peaks, one before flowering and other after flowering. The indices SR, NDVI, EVI, SAVI, and GNDVI were able to characterize changes in the canola canopy over time, as a function of phenological phases, weather conditions, and nitrogen fertilization, throughout the development cycle. Plant growth and development, variations in crop management, and environmental conditions affect the spectral response of canola

Análise de trilha em caracteres produtivos de Pennisetum sob corte em Itambé, Pernambuco Path analysis in productive characters of Pennisetum under cut in Itambé-PE

Objetivou-se obter estimativas de coeficientes de correlação genética e avaliar os desdobramentos das correlações em efeitos diretos e indiretos (análise de trilha) das variáveis independentes explicativas sobre a produção de matéria seca (variável dependente principal) em cinco clones de capim-elefante. Foram realizados cinco cortes a cada 60 dias nas condições edafoclimáticas da Zona da Mata de Pernambuco. Cada parcela experimental apresentou 24 m², com 2 m² de área útil. Houve alta correlação entre quase todas as variáveis explicativas e a variável principal. Entretanto, a característica número de lâminas foliares por perfilho explicou melhor o potencial de produção de matéria seca e atuou de forma direta e indireta sobre as variáveis explicativas.<br>This work aimed to estimate the correlation coefficients, determining the direct and indirect effects (path analysis) of explanatory independent variables on total dry matter production (main dependent variables) of five elephant grass clones in five cuts accomplished at the forest zone of Pernambuco. Each experimental plot measured 24 m² with 2 m² of utile area. There was high correlation between almost all the independent variables and the main variable. The characteristic leaf blade number per tiller, however, explained better the potential of dry matter production and leaf blade dry matter production, acting, respectively, in a direct and indirect way on the explanatory variables